Refining the termination age of the Cryogenian Sturtian glaciation in South China

Abstract

Zhou et al. (2004) reported a zircon U-Pb isotope dilution – thermal ionization mass spectrometry (ID-TIMS) age of 662.9 ± 4.3 Ma from the basal Datangpo Formation of the Cryogenian System in South China. It was the first zircon U-Pb age to constrain both the termination of Sturtian glaciation and the onset of Marinoan glaciation, despite its much larger uncertainty expected for modern ID-TIMS analysis. In this study, we carried out U-Pb chemical abrasion – isotope dilution – isotope ratio mass spectrometry (CA-ID-IRMS) analysis on the same sample, yielding a precise 206Pb/238U date of 659.96 ± 0.46 Ma. Bayesian eruption age estimate indicates that the ash layer was most likely deposited at 659.23 ± 1.24 Ma. The present study suggests that the Sturtian glaciation terminated before ∼660 Ma. Together with previously reported radiometric dates, the precise U-Pb age presented herein helps refine the current Cryogenian chronology.